Abstract
The establishment of a single validated endoscopic laryngeal grading system for assessing recurrent laryngeal neuropathy (RLN) is desirable to facilitate direct comparisons between the findings of different clinical and research groups worldwide. The objective of this study was to assess the relationship between the Havemeyer endoscopic laryngeal grading system and histopathological changes consistent with RLN in the left cricoarytenoideus dorsalis (CAD) muscle of horses of different breeds with a full range of clinical severities of RLN, i.e., from normal endoscopic laryngeal function to complete laryngeal hemiplegia. Endoscopic grading of laryngeal function of 22 horses was performed using the Havemeyer endoscopic laryngeal grading system. A biopsy sample of the left CAD muscle was obtained from each horse, either at post mortem examination (n = 16), or during routine laryngoplasty surgery (n = 6). A semi-quantitative histopathological scoring system was used to grade the severity of histopathological lesions consistent with RLN in the left CAD muscle of each horse. A significant positive correlation (rs = 0.705, p < 0.001) was found between the Havemeyer grades and sub-grades of laryngeal function and the semi-quantitative assessment of histopathological lesions consistent with RLN in the left CAD muscle. However, a wide spread of muscle histopathological scores was obtained, particularly from horses with Havemeyer sub-grades II.1, III.1 and III.2. In conclusion, the Havemeyer endoscopic laryngeal grading system was found to broadly correlate with histopathological changes consistent with RLN in equine cricoarytenoideus dorsalis muscle.
Highlights
Unilateral partial or total paralysis of the larynx has been recognised as an important equine upper respiratory tract disease for over two centuries (Fleming 1889), and is a significant cause of poor exercise performance in affected horses (Cole 1946; Derksen et al 1986)
The purpose of this study was to examine the correlation between the various Havemeyer grades and sub-grades of laryngeal function, and the degree of histopathological changes consistent with recurrent laryngeal neuropathy (RLN) present in the left cricoarytenoideus dorsalis (CAD) muscle of horses with the full range of clinical severities, i.e., from normal endoscopic laryngeal function to complete laryngeal hemiplegia
The independently-assessed, resting Havemeyer grades and sub-grades allocated to left laryngeal function of the horses by both assessors did not significantly differ (P=0.999)
Summary
Unilateral partial (hemiparesis) or total (hemiplegia) paralysis of the larynx has been recognised as an important equine upper respiratory tract disease for over two centuries (Fleming 1889), and is a significant cause of poor exercise performance in affected horses (Cole 1946; Derksen et al 1986). The most common type of equine laryngeal paralysis, i.e., recurrent laryngeal neuropathy (RLN), is caused by a distal axonopathy, predominantly affecting the left recurrent laryngeal nerve (Duncan et al 1974, 1978; Cahill and Goulden 1986 a,b; Duncan and Hammang 1987) This disorder results in denervation atrophy and consequent dysfunction of the intrinsic muscles of the larynx innervated by this nerve (Duncan et al 1977; Griffiths 1991). The purpose of this study was to examine the correlation between the various Havemeyer grades and sub-grades of laryngeal function, and the degree of histopathological changes consistent with RLN present in the left cricoarytenoideus dorsalis (CAD) muscle of horses with the full range of clinical severities, i.e., from normal endoscopic laryngeal function to complete laryngeal hemiplegia
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